Lipids and their constituent fatty acids play essential and dynamic roles in the maintenance of optimum growth, feed efficiency and health of fish species. Lipids are primarily included in formulated diets to maximize their protein sparing effects. However, increasing the concentration of dietary fatty acids (EPA and DHA) in the fish diet can negatively affect fish immune response. In this study, some immune parameters were evaluated in European Sea Bass, Dicentrarchus labrax fed by a diet (50% crude protein) supplemented with fish oil at levels of 13–22%. In a 50-day feeding trial, 12 plastic tanks (80-L) were stocked with 18 fish per tank (~8g). The results showed that lysozyme and myeloperoxidase significantly decreased in fish fed diets with 16-22% fish oil inclusion. In conclusion, high–fat diets negatively affected some immune parameters of Sea Bass. Further studies are encouraged on the effect of dietary levels of fish oil on disease resistance.